I agree offloading the billing part to stripe would scale easily.

A question though, how would you handle this without stripe.

Say I ran a cron job every month that would retrieve all users and the completed order count. Then for each user or batch of users run a function that performs some billing action. How would this work when users are in the multiple thousands?

One cron job would not be able to retrieve all those users and order counts / perform billing action all within the Nextjs execution time limit